In order to increase efficiency of a wireless communication system, it is essential to know channel quality. Quality of a downlink channel is reported by a base station to a user equipment. An indicator for indicating the channel quality is called a channel quality indicator (CQI) or a channel state indicator (CSI).
The CQI may be a value obtained by quantizing a channel state (e.g., a signal to interference-plus-noise ratio (SINR), a carrier to interference and noise ratio (CINR), a bit error rate (BER), and a frame error rate (FER)) or a modulation and coding scheme (MCS) index in an MCS table. In addition, the CQI may include a rank indicator (RI) and/or a precoding matrix indicator (PMI) in a multi-antenna system.
Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a promising next-generation mobile communication standard.
In a typical wireless communication system, one component carrier is considered in general even if a bandwidth is differently set between an uplink and a downlink. In 3rd 3GPP LTE, one carrier constitutes each of the uplink and the downlink on the basis of a single carrier, and the bandwidth of the uplink is symmetrical to the bandwidth of the downlink in general.
However, except for some areas of the world, it is difficult to allocate frequencies of wide bandwidths. Therefore, as a technique for effectively using fragmented small bands, a spectrum aggregation technique is being developed to obtain the same effect as when a band of a logically wide bandwidth is used by physically aggregating a plurality of bands in a frequency domain.
The spectrum aggregation includes a technique for supporting a system bandwidth of 100 mega Hertz (MHz) by using multiple carriers even if, for example, the 3GPP LIE supports a bandwidth of up to 20 MHz, and a technique for allocating an asymmetric bandwidth between the uplink and the downlink.
The 3GPP LTE is designed to report channel quality on the basis of a single-component carrier. However, with the introduction of multiple carriers, there is a need for a method capable of reporting channel quality in a multi-carrier system.